A-D-A-Type Porphyrins for Single-Component Organic Solar Cells

Two conjugated A-D-A (A = electron acceptor, D = electron donor) porphyrins 2OH-2BT-ZnPOR and 2C60-2BT-ZnPOR are designed and synthesized for single-component organic solar cells (SCOSCs). In the two molecules, two benzothiadiazoles (BTs) are connected to a porphyrin core as the electron-withdrawing units through pi-bridges to build a conjugated A-D-A main chain, which can narrow the energy levels, broaden the absorption, and promote the intramolecular charge transfer of the porphyrins. While there are no other electron-acceptor side groups in 2OH-2BT-ZnPOR, two fullerene units are symmetrically connected to 2OH-2BT-ZnPOR in 2C60-2BT-ZnPOR. Though the 2OH-2BT-ZnPOR-based SCOSCs exhibit a very poor device performances, the 2C60-2BT-ZnPOR-based SCOSC shows a power conversion efficiency (PCE) of 1.51% and a high open-circuit voltage (V-OC) of 1.05 V, which is also much higher than those of previously reported porphyrin-based SCOSCs. The much higher performance of 2C60-2BT-ZnPOR SCOSCs can be ascribed to the delocalized pi-electrons induced by the conjugated A-D-A main chain and the promoted charge dissociation induced by the fullerene units in 2C60-2BT-ZnPOR.